Articles of this kind are known which can be put into one configuration wherein the two elements are temporarily held rigidly fixed relative to one another and which may be easily brought, from the configuration in which they are held in a rigid state, into a configuration in which the two elements are free to rotate relative to one another, the configuration in which they are held in a rigid state puffing, for example. The two elements in a relative position such that it is particularly easy to mount the article on the support which is meant to receive it, and the article being brought into the normal articulation configuration once the operation of mounting on the support has been completed.